1. Field of the Invention
The present invention relates to a mask for transferring a pattern and manufacturing method thereof, and more particularly, to a mask for transferring a pattern for use in a semiconductor device.
2. Description of the Background Art
A conventional mask for transferring a pattern for use in a semiconductor device (hereinafter referred to as a "mask") is disclosed, for example, in J: Vac. Sci. Technol. B, Vol. 10, No. 6, pp. 2480-2485 (1992) by Akira Chiba, Shuichi Matsuda, and Yaichiro Watakabe. FIG. 16 is a sectional view showing the conventional mask disclosed. Referring to FIG. 16, in the conventional mask 100, an optically opaque light-shielding film 102 is formed on a prescribed region of a surface of an optically transparent mask substrate 101. On light-shielding film 102, an antireflection film 103 for reducing light reflectance of mask substrate 102 is formed. Mask substrate 101, light-shielding film 102 and antireflection film 103 are formed, for example, of a quartz glass substrate, a molybdenum silicide (MoSi) film and a molybdenum silicide oxide film, respectively.
A method of using the above-described conventional mask 100 will now be described. First, a resist (not shown) is formed on a semiconductor substrate (not shown). Then, for example, ultraviolet is directed to the resist through mask 100. Since ultraviolet passes only through a region where light-shielding film 102 does not exist, a region in the resist corresponding to light-shielding film 102 is not irradiated with ultraviolet. Consequently, there exist regions irradiated and not irradiated with ultraviolet. That is, there exist regions exposed and not exposed to ultraviolet in the resist. The exposed region or the unexposed region is then removed with developer. Thus, a resist pattern is formed. A resist pattern is formed for each manufacturing step of a semiconductor device by using mask 100 in this manner.
FIGS. 17-20 are sectional views showing a manufacturing process of the conventional mask shown in FIG. 16. A manufacturing method of the conventional mask will now be described with reference to FIGS. 17-20.
First, as shown in FIG. 17, a light-shielding film 102a made of a MoSi film is formed on mask substrate 101, using sputtering and vacuum evaporation. An antireflection film 103a made of a molybdenum silicide oxide film is formed on light-shielding film 102a by the oxidizing light-shielding film (molybdenum silicide film) 102a. A photo-sensitive polymer film (resist) 104a is formed on antireflection film 103a.
Then, as shown in FIG. 18, a mask pattern is formed on resist 104a by directing an electron beam 105 to a prescribed region of resist 104a. A resist pattern 104 shown in FIG. 19 is then formed by performing a developing process.
Then, patterned antireflection film 103 and light-shielding film 102 as shown in FIG. 20 are formed by etching antireflection film 103a and light-shielding film 102a using resist pattern 104 as a mask. Finally, the conventional mask shown in FIG. 16 is completed by removing resist 104.
In the above-described manufacturing process of the conventional mask, however, there are the following problems. That is, in a step shown in FIG. 18, when electron beam 105 is directed to resist 104a, diameter of electron beam 105 can not be reduced due to the restriction of the optical system. More specifically, it is difficult to reduce the diameter of electron beam 105 to about 40 .ANG. or less. Therefore, conventionally, it is difficult to form fine resist pattern 104. Consequently, it has been difficult to form a fine circuit pattern of light-shielding film 102.
As a result, methods using Scanning Tunneling Microscope (STM) instead of the electron beam have been proposed as a method to expose a resist. These are disclosed, for example, in C. R. K. Marrian and E. A. Dobisz: Ultramicroscopy Vol. 42-44, pp. 1309-1316 (1992).
FIG. 21 schematically shows the conventionally proposed method of exposing a resist using STM. Referring to FIG. 21, a voltage of 10 V or less is applied between a probe 106 of STM and light-shielding film 102a and antireflection film 103a. In this proposed example, resist 104a is exposed to electrons emitted from probe 106 of STM. Since diameter of an electron current emitted from probe 106 is about 1 .ANG. or less, finer resist pattern can be formed compared to that in the method using the electron beam shown in FIG. 18.
In the conventionally proposed method, however, electrons emitted from probe 106 are scattered within resist 104a and are scattered due to their collision with antireflection film 103a. These phenomena are referred to as proximity effect. If the above-described scattering of electrons occurs, a region which is not to be exposed could also be exposed. Therefore, accuracy of the resulting resist pattern decreases and finer resist pattern cannot be formed.
In addition, in the conventional mask, light-shielding film (molybdenum silicide film) 102 and antireflection film (molybdenum silicide oxide film) 103 can easily be damaged mechanically during use. Since light-shielding film (molybdenum silicide film) 102 is formed by sputtering or vacuum evaporation, molybdenum silicide film 102 is made of a polycrystalline film which includes a collection of fine crystal grains. Accordingly, molybdenum silicide film (light-shielding film) 102 can easily be deformed if external force is applied during use.
Antireflection film (molybdenum silicide oxide film) 103 on light-shielding film (molybdenum silicide film) 102 is formed by oxidizing light-shielding film (molybdenum silicide film) 102 made of a polycrystalline film which is a collection of fine crystal grains. Therefore, quality of antireflection film (molybdenum silicide oxide film) 103 reflects that of light-shielding film (polycrystalline film) 102. Consequently, it is difficult to form dense antireflection film 103. Accordingly, conventional antireflection film 103 can easily be deformed if the external force is applied during use. Conventionally, it is difficult to increase the number of times the mask can be used, since light-shielding film (molybdenum silicide film) 102 and antireflection film (molybdenum silicide oxide film) 103 can easily be deformed during use.